A coating die is used to apply a thin layer of liquid material (e.g., thermoplastic or solvent based) to a support substrate such as a sheet or film. The most common coating process is to provide a continuous layer of coated material on the substrate by having a continuous stream of material applied to the moving substrate. However, occasionally it is desired to coat a strip or patch of material, the patch having a specific length, with uncoated areas therebetween. Such ‘patch coating’ is often desired for applications such as adhesive labels, batteries (e.g., lithium ion batteries), and for biological studies. For these instances, the application of the coating material is temporarily stopped or interrupted while the substrate continues to move, providing an area of un-coated substrate around the perimeter of the coating.
One attempt to provide an apparatus that can temporarily stop the flow of coating material is described in U.S. Pat. No. 4,756,271 to Maier. This patent describes a coating die that includes a rotatable cam inside, which can be rotated among different fluid chambers to select different materials or to interrupt the coating during web movement.
Another attempt to provide an apparatus that can temporarily stop the flow of coating material is described in U.S. Pat. No. 4,725,468 to McIntyre. This patent describes a method of co-extruding a discontinuous or sectioned coating over a continuous coating. A 3-way poppet valve (such as described in U.S. Pat. No. 4,565,217) can be intermittently shuttered by an electronic control circuit to control the flow of the discontinuous material.
These designs, however, can be problematic for high speed coating, because the on and off flow stopping is not fast enough or sufficiently accurate for short un-coated distances between patches. There is always room for improvement.